Problem with Defiant digital timer

I have recently purchased an in-wall digital timer to replace my standard light switch that controls my porch lights. I installed it per instructions and it appears to power up correctly, but when I turn on the switch, the lights start rapidly flashing on and off. What have i done wrong?

One of the Defiant timers did not require a neutral wire to be in the switch box. That particular model will NOT work LED or CFL lamps because to operate lets a very small amount of electricity through the circuit. That wasn't a problem with incandescent lamps but causes weird behavior in LED and CFL lamps. If you don't have a neutral, then you will have to use an incandescent lamp in your fixture.

If that's not problem, then the timer is likely defective and needs to be replaced.